Battery Management System Applying Embedded Impedance Measurement
Lignell, Leevi (2023)
Lignell, Leevi
2023
Sähkötekniikan DI-ohjelma - Master's Programme in Electrical Engineering
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2023-06-15
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202306056501
https://urn.fi/URN:NBN:fi:tuni-202306056501
Tiivistelmä
The use of lithium-ion batteries is continuously increasing due to the need to de crease carbon emissions. Lithium-ion batteries are the main electrical energy storage system in electric vehicles and they can also be used in load balancing with renew able energy sources. Safe and effcient use of lithium-ion batteries is ensured by a battery management system that monitors the battery’s state and controls its use.
Battery management systems monitor the battery system’s state with diferent parameters. Most signifcant are the state of health (SOH) and state of charge (SOC). They are the measures of the decay in battery’s total capacity and the charge available in the battery, respectively. Typically, it is diffcult to measure these parameters directly and many methods for their evaluation have been developed. One of the methods is to measure the battery internal impedance which is shown to be linked to the SOH and SOC.
This thesis examines broadband methods to measure the battery impedance. In the methods, a broadband excitation such as the pseudo-random binary sequence (PRBS) is applied to perturb the battery under test and Fourier techniques are then used to compute the impedance. A broadband perturbation has energy at several frequencies making it possible to rapidly obtain the battery impedance. This thesis also shows a simple impedance-data-based SOC-estimation method. All the presented methods are verifed with experimental measurements using commercial Li-ion batteries.
Battery management systems monitor the battery system’s state with diferent parameters. Most signifcant are the state of health (SOH) and state of charge (SOC). They are the measures of the decay in battery’s total capacity and the charge available in the battery, respectively. Typically, it is diffcult to measure these parameters directly and many methods for their evaluation have been developed. One of the methods is to measure the battery internal impedance which is shown to be linked to the SOH and SOC.
This thesis examines broadband methods to measure the battery impedance. In the methods, a broadband excitation such as the pseudo-random binary sequence (PRBS) is applied to perturb the battery under test and Fourier techniques are then used to compute the impedance. A broadband perturbation has energy at several frequencies making it possible to rapidly obtain the battery impedance. This thesis also shows a simple impedance-data-based SOC-estimation method. All the presented methods are verifed with experimental measurements using commercial Li-ion batteries.